Interaction of the cardiovascular risk marker asymmetric dimethylarginine (ADMA) with the human cationic amino acid transporter 1 (CAT1)

Abstract

Elevated plasma concentrations of endogenously formed asymmetric (ADMA) and symmetric dimethyl-l‐arginine (SDMA) are associated with adverse clinical outcomes. Our aim was to investigate the cellular uptake properties of ADMA by the human cationic amino acid transporter 1 (CAT1; SLC7A1).Human embryonic kidney cells (HEK293) stably overexpressing CAT1 (HEK-CAT1) and vector-transfected control cells (HEK-VC) were established to determine cellular uptake of labeled [3H]ADMA and [3H]l-arginine.Uptake of ADMA and l-arginine were significantly (p<0.001) higher in HEK-CAT1 than in HEK-VC at all investigated concentrations. Apparent Vmax values of cellular ADMA and l-arginine uptake by CAT1 were 26.9±0.8 and 11.0±0.2nmol mg protein−1 min−1, respectively. Km values were 183±21μmoll−1 (ADMA) and 519±36μmoll−1 (l-arginine). Uptake of ADMA was inhibited by l-arginine and SDMA with IC50 values (95% CI) of 227 (69–742) μmoll−1 and 273 (191–390) μmoll−1, respectively. ADMA and SDMA inhibited CAT1-mediated uptake of l-arginine with IC50 values of 758 (460–1251) μmoll−1 and 789 (481–1295) μmoll−1, respectively. Efflux of ADMA was significantly increased in HEK-CAT1 cells as compared to HEK-VC (p<0.05).CAT1 mediates the cellular uptake of ADMA. In its physiological concentration range ADMA is unlikely to impair CAT1-mediated transport of l-arginine. Conversely, high (but still physiological) concentrations of l-arginine can inhibit CAT1-mediated cellular uptake of ADMA.